Prevalence of GJB2 mutations in prelingual deafness in the Greek population

OBJECTIVE: Mutations in the gene encoding the gap junction protein connexin 26 (GJB2) have been shown as a major contributor to prelingual, sensorineural, nonsyndromic, recessive deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations. The aim of our study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in the Greek population. METHODS: In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific polymerase chain reaction (PCR) for the detection of the 35delG mutation. Patients heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene. RESULTS: The 35delG mutation was found in 42.2% of the chromosomes in 45 familial cases of prelingual, nonsyndromic deafness (18 homozygotes and 2 heterozygotes) and in 30.6% of the chromosomes in 165 sporadic cases (45 homozygotes and 11 heterozygotes). Direct genomic sequencing in heterozygous patients revealed the L90P (2 alleles), W24X (2 alleles), R184P (2 alleles), and 291insA (1 allele) mutations. CONCLUSION: Mutations in the GJB2 gene are responsible for about one third of prelingual, sensorineural, nonsyndromic deafness in the Greek population, and allele-specific PCR is an easy screening method for the common 35delG mutation.     

Sudden hearing loss in a family with GJB2 related progressive deafness

Mutations of GJB2, the gene encoding connexin 26, have been associated with prelingual, sensorineural hearing loss of mild to profound severity. One specific mutation, the 35delG, has accounted for the majority of mutations detected in the GJB2 gene in Caucasian populations. Recent studies have described progression of hearing loss in a proportion of cases with GJB2 deafness. We report an unusual family with four 35delG homozygous members, in which the parents were deaf-mute whilst both children had a postlingual progressive hearing loss. Furthermore, the son suffered from sudden hearing loss.     

The novel c.247_249delTTC (p.F83del) GJB2 mutation in a family with prelingual sensorineural deafness

Non-syndromic hearing loss is one of the most common hereditary determined diseases in human, and the disease is a genetically heterogeneous disorder. Mutations in the GJB2 gene, encoding connexin 26 (Cx26), are a major cause of non-syndromic recessive hearing impairment in many countries and are largely dependent on ethnic groups. Due to the high frequency of the c.35delG GJB2 mutation in the Greek population, we have previously suggested that Greek patients with sensorineural, non-syndromic deafness should be tested for the c.35delG mutation and the coding region of the GJB2 gene should be sequenced in c.35delG heterozygotes. Here we present on the clinical and molecular genetic evaluation of a family suffering from prelingual, sensorineural, non-syndromic deafness. A novel c.247_249delTTC (p.F83del) GJB2 mutation was detected in compound heterozygosity with the c.35delG GJB2 mutation in the proband and was later confirmed in the father, while the mother was homozygous for the c.35delG GJB2 mutation. We conclude that compound heterozygosity of the novel c.247_249delTTC (p.F83del) and the c.35delG mutations in the GJB2 gene was the cause of deafness in the proband and his father.     

Prevalence of the GJB2 mutations and the del(GJB6-D13S1830) mutation in Brazilian patients with deafness

Mutations in the GJB2 gene are the most common cause of sensorineural non-syndromic deafness in different populations. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in many countries. The aim of this study was to determine the prevalence of GJB2 mutations and the del(GJB6-D13S1830) mutation in non-syndromic deaf Brazilians. The 33 unrelated probands were examined by clinical evaluation to exclude syndromic forms of deafness. Mutation analysis in the GJB2 gene and the testing for the del(GJB6-D13S1830) were performed in both the patients and their family members. The 35delG mutation was found in nine of the probands or in 14 of the mutated alleles. The V37I mutation and the del(GJB6-D13S1830) mutation were also found in two patients, both are compound heterozygote with 35delG mutation. These findings strengthen the importance of genetic diagnosis, providing early treatment, and genetic counseling of deaf patients.     

Non-invasive screening for GJB2 mutations in buccal smears for the diagnosis of inherited hearing impairment

BACKGROUND: Approximately 1 out of 1000 children is affected by severe or profound hearing impairment at birth. In the last years it has been shown that more than 50 % of inherited prelingual, sensorineural hearing impairment may be attributed to genetic defects. Most commonly, the GJB2 gene (chromosome 13q11) that encodes connexin 26 (Cx26) is affected. Cx26 is crucial for the formation of gap junctions which play an important role in the intercellular exchange of electrolytes. A variety of autosomal recessive GJB2 mutations associated with inherited hearing impairment has meanwhile been identified. The most common GJB2 mutation in Caucasian populations, 35delG accounts for the majority of cases and has a carrier frequency of more than 2.5 %. Other distinct mutations account for hearing impairment in other parts of the world. MATERIAL AND METHODS: We examined in 59 Caucasian and Ghanaian individuals whether DNA recovered from buccal smears was appropriate for genetic testing by polymerase-chain reaction (PCR) based DNA-sequencing. RESULTS: Buccal smears could be taken conveniently in all cases, even from small babies. In 53 out of 59 samples the material recovered from buccal smears could be subjected to PCR of the second exon of the GJB2 gene and subsequent DNA-sequencing. GJB2 mutations were identified in 34 patients. 13 Caucasian individuals exhibited the most common mutation 35delG. In addition, four cases of the rare W24X and each one heterozygous case of the V153I- and the L90P mutation were found. In two African individuals the 35insG mutation was detected. All other African patients had mutations exclusively identified in Ghana so far with the exception of R143W. R143W accounts for most cases of profound deafness in Ghana and has been identified in low frequencies in other ethnic groups as well. CONCLUSION: Screening for GJB2 mutations in DNA recovered from buccal smears of individuals with inherited hearing impairment offers an easy, non-invasive method for early diagnosis and a basis of genetic counselling.     

Prevalence of 35de1G/GJB2 and del (GJB6-D13S1830) mutations in patients with non-syndromic deafness from a population of Espírito Santo - Brazil

Mutations in GJB2 gene are the leading cause of deafness in autosomal recessive inheritance, and the 35delG mutation is the most common in many ethnic groups. Besides the 35delG mutation in homozygosis, the mutation is also found in compound heterozygosis, coupled with other mutations in genes GJB2 and GJB6.AimTo determine the prevalence of 35delG/GJB2 and del (GJB6-D13S1830) mutations in patients with sensorineural hearing impairment in residents from the Espirito Santo state, Brazil.Materials and methods77 unrelated individuals with moderate to profound sensorineural hearing loss were evaluated. The 35delG mutation was studied by PCR / RFLP; and the del (GJB6-D13S1830) mutation was screened by the technique of multiplex PCR.Results88.3% had normal genotype for the studied mutations, 1.3% were compound heterozygotes, 3.9% homozygotic for the 35delG mutation, 6.5% heterozygotic for 35delG/GJB2. The frequency of 35delG/GJB2 and del (D13S1830/GJB6) alleles in the sample was 7.8% and 0.65%, respectively.ConclusionThe data confirmed the existence of the mutations studied in cases of sensorineural hearing loss in a population from Espírito Santo / Brazil. These findings reinforce the importance of genetic diagnosis, which can provide early treatment for children and genetic counseling for the affected families.     

GJB2 mutations in Turkish patients with ARNSHL: prevalence and two novel mutations

Mutations in the connexin 26 gene (GJB2) cause a significant proportion of prelingual non-syndromic autosomal recessive deafness in all populations studied so far. To determine the percentage of hearing loss attributed to GJB2 in northeast Turkey, 93 unrelated patients with autosomal recessive non-syndromic hearing loss (ARNSHL) were screened. Seven different mutations were found in 29 of the patients with severe to profound hearing loss. The 35delG mutation was the most common mutation, accounting for 76% of all mutant GJB2 alleles. Four already described mutations, W24X, 310del14, delE120 and R184P and two novel mutations, Q80K and P173S, were identified. The allelic Delta(GJB6-D13S1830), which can cause hearing loss in combination with GJB2 mutations, was not present in our patients. Our results are comparable to those reported in other regions in Turkey and indicate that GJB2 mutations account for about 30% of Turkish patients with ARNSHL. Besides 35delG, W24X and delE120 occur more than once in the Turkish ARNSHL population with a frequency of about 5%.     

散发感音神经性聋患者中GJB2基因突变检测的临床意义

目的探讨散发感音神经性聋患者中GJB2基因突变检测的临床指导意义.方法运用聚合酶链反应对解放军总医院听力诊断中心收集的242例散发感音神经性聋患者(135例语前聋患者,107例语后聋患者)的GJB2基因编码区进行扩增,扩增产物纯化后直接测序分析.结果 135例语前聋患者中GJB2基因致病突变的复合杂合和纯合个体有26例,占语前聋个体的19.26%;107例语后聋患者中未发现复合杂合和纯合致病突变,仅发现3例235delC杂合突变携带者、1例176del16杂合突变携带者.结论语前聋者GJB2基因致病突变阳性率明显高于语后聋患者,语前聋患者常规进行GJB2基因检测可从基因水平明确诊断,并为耳聋患者提供重要遗传信息.     

Determination of the carrier frequency of the common GJB2 (connexin-26) 35delG mutation in the Greek Cypriot population

OBJECTIVE: Mutations in the GJB2 (connexin-26) gene are responsible for more than half of all cases of prelingual recessive inherited non-syndromic deafness in Europe. One specific mutation 35delG, accounts for up to 70% of the mutations detected in European populations and is one of the most frequent disease mutations identified so far. The aim of this study is to determine the percentage of carriers of this mutation in the Greek Cypriot population. METHODS: Genomic DNA was isolated from a total of 405 healthy unrelated Greek Cypriot adults. Screening for the frameshift 35delG mutation was performed by using an allele-specific PCR protocol. Moreover, using the Poisson probability distribution, we compared the carrier frequencies of the 35delG mutation of the Greek Cypriot population to the various European and Middle Eastern populations. RESULTS: The carrier frequency in the Greek Cypriot population was estimated to be 2.5% and is similar to that observed in other European populations. The variance estimate for 35delG mutation produces slightly wider intervals with the Poisson model when compared with Binomial probability variance estimate.     

Connexin 26 mutations and nonsyndromic hearing impairment in northern Finland

OBJECTIVE: The aims of the present study were to evaluate the role of the gap junction protein beta-2 gene (GJB2), encoding connexin 26 (Cx26), in children with moderate to profound prelingual nonsyndromic sensorineural hearing impairment (HI) and to investigate the carrier frequencies of the GJB2 gene mutations in a control population in Northern Finland. METHODS: Mutation analysis was performed by direct sequencing and carrier detection by conformation sensitive gel electrophoresis further confirmed by direct sequencing. RESULTS: Cx26 mutations were found in 15 of 71 (21.1%) (67 families) children with HI. Homozygosity for the mutation 35delG was shown to be the cause of HI in 13 of 15 (86.7%) children. Homozygosity for the M34T genotype was found in one child, and compound heterozygosity for the M34T/V37I genotype was found in another. Five families of those with suspected familial HI (29.4%) and six families out of those with sporadic HI (12.0%) had a homozygous or compound heterozygous mutation. The carrier frequency for the mutation 35delG was 1 of 78 (4 of 313) and that for the M34T was 1 of 26 (12 of 313). CONCLUSION: 35delG/35delG genotype was found to be a significant cause of moderate to profound prelingual nonsyndromic sensorineural HI in Northern Finland. M34T/M34T genotype was seen in only one child, but the carrier frequency of the M34T allele was about three times higher than that of the 35delG mutation.     

Carrier frequency of the 35delG and A1555G deafness mutations in the Argentinean population. Impact on the newborn hearing screening

OBJECTIVE: Hearing loss is a complex multifactorial disorder caused by genetic and environmental factors. The 35delG mutation in the GJB2 gene is the most prevalent mutation in Caucasian patients with genetic sensorineural deafness. The A1555G mutation in the mitochondrial 12S rRNA is the main genetic alteration associated with aminoglycoside-induced deafness. The aim of this study was to evaluate the prevalence of both mutations in general population of Argentina. METHODS: A total of 712 samples of unrelated healthy blood donors and 330 newborn dried blood spots were studied by PCR-RFLP. RESULTS: The 35delG mutation was detected in 11/ 712 unrelated blood donors. The carrier frequency found in this sample (1/65) proved to be lower than that found in Southern European countries, mainly Spain and Italy, from where Argentina originally received its major immigration waves. When the populations of Southern Europe were considered altogether, this difference reached statistical significance. The A1555G mutation was not found in any of the 1042 samples tested. CONCLUSIONS: Taking into account the 35delG carrier frequency found in this study, it could be estimated that 130-160 children with congenital deafness due to mutations in the connexin genes would be born per year in Argentina. In contrast, the mitochondrial mutation A1555G appears to be infrequent in general Argentinean population.     

Management of difficult airway in intratracheal tumor surgery

Background

C.35delG/GJB2 mutation is the most frequent genetic cause of deafness in Caucasians. Another frequent mutation in some Caucasian populations is del(GJB6-D13S1830). Both GJB2 and GJB6 genes belong to the same DFNB1 locus and when the two mutations are found in combination in a hearing-impaired person, a digenic pattern of inheritance is suggested.

Methods

We examined 63 Croatian subjects (25 familial and 38 sporadic cases) with prelingual non-syndromic hearing impairment by polymerase chain reaction for the presence of the c.35delG/GJB2 and the del(GJB6-D13S1830) mutations.

Results

Of the 63 unrelated hearing-impaired subjects, the mutation c.35delG/GJB2 was found in 21 subjects (33.3%). In 5 of them the mutation was found in the heterozygous state, all of them being compound heterozygotes, as sequencing revealed a second mutation within the coding region of the gene in 3 subjects, and a splice site mutation in 2 subjects. The del(GJB6-D13S1830) mutation was not found in the investigated hearing-impaired Croatian subjects.

Conclusion

Our results contribute to the knowledge of geographic distribution and population genetics of the GJB2 and GJB6 mutations in the Europeans.     

Longitudinal phenotypic analysis in patients with connexin 26 (GJB2) (DFNB1) and connexin 30 (GJB6) mutations

In 15 Belgian subjects with prelingual sensorineural hearing impairment, the connexin 26 (GJB2) gene and the connexin 30 (GJB6) gene were analyzed for the presence of the 35delG mutation and the delta(GJB6-D13S1830) deletion first described by del Castillo et al in 2002. Seven patients were found to be homozygous for the 35delG mutation; 7 were combined heterozygotes for the 35delG mutation and the GJB6 deletion. In 11 subjects, phenotype and genotype were correlated. Significant, transient progression, in the range of 1.7 to 2.7 dB/y, was only found in 2 patients in the first part of the second decade of life. Hearing impairment was otherwise stable, with mean thresholds of 75, 90, and 100 dB at 0.125, 0.25, and 0.5 kHz, respectively, and 100 dB or higher at 1 to 4 kHz. There was no significant difference in hearing impairment between the patients with the homozygous 35delG mutation in GJB2 and those who are heterozygous for both the 35delG mutation and the deletion encompassing part of GJB6.     

Connexin 26基因233delC突变与中国人先天性耳聋的研究

目的 :Connexin2 6基因突变是引起常染色体隐性遗传 DFNB1和常染色体显性遗传 DFNA3的遗传基础 ,其中的 35 del G的突变在欧美人 DFNB1耳聋患者中的检出率为 70～ 80 % ,但在中国耳聋人群中未检到该点突变。本文旨在筛选中国人耳聋相关的 Connexin2 6基因的突变热点。方法 :采用 PCR- RFL P筛选 2 19例不同耳聋类型的患者和 5 0例听力正常人的 Connexin 2 6基因 2 33del C的突变 (2 1.5 % )。结果 :2 19例耳聋患者中共发现了 47例 Connexin 2 6基因2 33del C的突变 (2 1.5 % )。在先天性耳聋患者中 2 33del C的突变率为 33% ,遗传性语前聋患者为 2 6 .7%。 5 0例药物性致聋的患者有 10例发生突变。遗传性及散发性进行性感音神经性耳聋和听力正常人未检测到 2 33delc突变。结论 :Connexin2 6基因 2 33del C突变在中国先天性耳聋人群中发生频率较高 ,与欧美人不同。我们的结果表明 ,Connexin2 6基因异常导致耳聋的突变热点具有种族特异性     

Phenotype of patients showing hearing impairment based on the 35delG mutation in the connexin 26 gene

BACKGROUND: Hereditary hearing impairment constitutes a heterogeneous class of disorders showing different patterns of inheritance and involving multiple genes. Mutations in the GJB2 gene, especially the 35delG mutation, have been established as a major cause of inherited and sporadic nonsyndromic hearing impairment in different populations. METHODS: We analyzed 14 northeast Hungarian families and 69 sporadic cases with nonsyndromic hearing impairment for the 35delG mutation. Sixty-five patients showing a homozygous 35delG mutation were examined regarding their audiologic phenotype. RESULTS: In general, these patients (70%) showed a prelingual, sensorineural, bilateral, symmetric hearing impairment without progression. The audiograms demonstrated sloping as well as flat patterns. CONCLUSIONS: The severity of hearing impairment varied in 30% of all analyzed patients, making genetic counseling difficult.     

Prevalence of GBJ2 mutations in patients with severe to profound congenital nonsyndromic sensorineural hearing loss in Bulgarian population

Objective of the study is to assess the prevalence of Connexin 26 (GJB2) mutation in patients with congenital nonsyndromic sensorineural hearing loss in Bulgarian population. Study design is done prospectively. Patient inclusion criteria for this study were diagnosis of congenital nonsyndromic hearing loss, and absence of potential sibling relationships between patients included in the study (anamnestic pedigree for at least three generations). Patients were excluded from the study group if one of the following conditions were present: secondary hearing loss (cytomegalovirus, rubella, meningo-encephalitis, mastoiditis, other infections, posterior fossa tumors, etc.), exposure to drugs or other prenatal or perinatal etiology of deafness, and congenital syndromic hearing loss. Genomic DNA samples from whole blood were tested with sequence analysis for mutations in the coding region of the GJB2. Results state that 51 patients were analyzed for GJB2 mutations. Twenty of the patients (39%) with mutant alleles were homozygous for the c.35delG mutation (c.35delG/c.35delG) and four patients (8%) presented as heterozygotes (c.35delG/WT). In one patient, who carried a heterozygous mutation c.35delG, a second mutation was found—312del114. Additionally, in two other patients were discovered the mutations Trp24X (W24X) and, respectively, Arg127His(R127H), both in heterozygous states. From the whole study group there was only one patient with compound heterozygous genotype—p.Leu90Pro(L90P)/p.Ile121Asn. The latter one has never been reported in the literature so far. In conclusion, this study determines the importance of connexin 26 mutations in Bulgarian children with severe to profound congenital nonsyndromic sensorineural hearing loss, the prevalence of the different mutation variants and their relationship with the ethnical background of the patients. In addition, we report for the first time a novel mutation in the GJB2 gene.     

Prevalence of mutations located at the dfnb1 locus in a population of cochlear implanted children in eastern Romania

Objective

Hearing loss is one of the major public health problems, with a genetic etiology in more than 60% of cases. Connexin 26 and connexin 30 mutations are the most prevalent causes of deafness. The aim of this study is to characterize and to establish the prevalence of the GJB2 and GJB6 gene mutations in a population of cochlear implanted recipients from Eastern Romania, this being the first report of this type in our country.

Methods

We present a retrospective study that enrolled 45 Caucasian cochlear implanted patients with non-syndromic sensorineural severe to profound, congenital or progressive with early-onset idiopathic hearing loss. We performed sequential analysis of exon 1 and the coding exon 2 of the GJB2 gene including also the splice sites and analysis of the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

Results

The genetic analysis of the GJB2 gene identified connexin 26 mutations in 22 patients out of 45 (12 homozygous for c.35delG, 6 compound heterozygous and 4 with mutations only on one allele). We found 6 different mutations, the most prevalent being c.35delG - found on 32 alleles, followed by p.W24* - found on 2 alleles. We did not identify the deletions del(GJB6-D13S1830), del(GJB6-D13S1854) and del(chr13:19,837,343-19,968,698).

Conclusions

Although the most prevalent mutation was c.35delG (80% from all types of mutations), unexpectedly we identified 5 more different mutations. The presence of 6 different mutations on the GJB2 gene has implications in hearing screening programs development in our region and in genetic counseling.     

A study of GJB2 and delGJB6-D13S1830 mutations in Brazilian non-syndromic deaf children from the Amazon region

Hearing impairment affects about 1 in 1000 newborns. Mutations in the connexin 26 (GJB2) gene rank among the most frequent causes of non-syndromic deafness in different populations, while delGJB6-D13S1830 mutation located in the DFNB30 locus is known to cause sensorineural hearing loss. Despite the many studies on the involvement of GJB2 mutations in hearing impairment in different populations, there is little information on genetic deafness in Brazil, especially in the Amazon region.ObjectiveTo determine the prevalence of GJB2 mutations and delGJB6-D13S1830 in 77 sporadic non-syndromic deaf patients.MethodThe coding region of the GJB2 gene was sequenced and polymerase chain reaction was performed to detect the delGJB6-D13S1830 mutation.ResultsMutant allele 35delG was found in 9% of the patients (7/77). Mutations M34T and V95M were detected in two distinct heterozygous patients. Non-pathogenic mutation V27I was detected in 28.6% of the patients (22/77). None of the deaf patients carried the delGJB6-D13S1830 mutation.ConclusionMutant alleles on gene GJB2 were observed in 40% (31/77) of the subjects in the sample. Pathogenic variants were detected in only 12% (9/77) of the individuals. More studies are required to elucidate the genetic causes of hearing loss in miscegenated populations.     

Spectrum of GJB2 mutations causing deafness in the British Bangladeshi population

Objective: Mutations in Gap Junction Beta 2 (GJB2) (the gene encoding the protein Connexin 26) have been found to be a major cause of non‐syndromic sensorineural recessive deafness. The mutations in GJB2 causing hearing impairment vary in different populations. The aim of this study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in a population of Bangladeshi origin in the UK. Design: Cross‐sectional survey. Setting: Community based audiology clinic and tertiary level genetics department. Methods: Fifty‐three families (67 patients) with sensorineural hearing loss of unknown cause were included in the study. Detailed history and examination excluded syndromic and environmental causes of hearing loss in the subjects as far as possible. Genetic analysis was performed, specifically looking for mutations in the GJB2 gene. Results: Of the 53 families, 14 were confirmed to have biallelic pathogenic mutations in GJB2 (26%). The most common mutations of GJB2 in this population were W24X, IVS1+1, M1V, W77X and Q124X, W24X being the most common mutation seen in 57% of patients. Conclusion: Mutations in GJB2 are responsible for over one quarter of non‐syndromic sensorineural deafness in the British Bangladeshi population. It is recommended that all Bangladeshi patients with non‐syndromic hearing loss should be first tested for GJB2 mutations before requesting other aetiological investigations.     

Late postnatal onset of hearing loss due to GJB2 mutations

GJB2 mutations account for approximately 50% of recessive non-syndromic deafness, with 35delG being the most prevalent. Homozygous 35delG mutations cause pre-lingual, non-progressive hearing loss that is detected on newborn hearing screening programmes. We present a sibling pair with homozygous 35delG mutations, who passed hearing tests in early infancy and developed progressive sensorineural hearing loss, one requiring a cochlear implant. These cases illustrate that deafness due to such mutations may have a late onset and consequently be missed on neonatal screening programmes and they may present an argument to consider neonatal screening for GJB2 mutations in order to aid early intervention.